This invention relates to pH measurements. More particularly, this invention relates to a system for measuring the pH of a liquid containing oil and water.
In metalworking operations, such as, for example, rolling of a hot metal, such as aluminum, in a rolling mill, a liquid is applied to the rolls and/or the rolled stock which functions both as a coolant and a lubricant. Commonly such a liquid comprises an oil in water mixture wherein the oil may comprise a common lubricating oil or a mixture of oil and additives blended to achieve particular properties. In any event, it is important that the oil, which functions as the lubricant, remain dispersed in the water phase. However, during the course of use, such a coolant commonly becomes contaminated due to the introduction of metal ions and formation of products of oxidation, thermal and biological degredation. Such contamination may cause the pH of the coolant to change in an undesirable way resulting in the loss of lubricating properties. It is, therefore, desirable to monitor the pH of the coolant as it is used.
As is well known to those skilled in the art, normal pH measurements involve the immersion of a glass electrode attached to a pH meter into the liquid to be tested. However, the use of such a pH meter for the measurement of the pH of an oil in water mixture is complicated by the fouling of the glass electrode by deposition of a coating of oil on the surface of the electrode, thus upsetting the measurement. When such an arrangement is used, it is, therefore, necessary to periodically disassemble the apparatus to manually clean such depositions off the glass electrode. It would, therefore, be desirable to have a system whereby the pH of an oil in water mixture can be monitored without the need for periodic manual disassembly of the monitoring apparatus to clean the glass electrode.